When you are choosing a topic for your dissertation, you should consider your possibilities, your interests, and etc. Otherwise it would be an exhausting process that bothers you.
After finding out your interest area and making sure that you have access to the needs of research on it, start limiting the topic until it is a specified title which is suitable for a thesis.
In art, there are some topics that could be interesting to you. See the following examples, if one of them seems attractive to you, do not forget to limit it until it is clearly defined, so that it is suitable as an art thesis topic
African visual art
The continent of Africa has a long history and could be a good title for your thesis. Ancient Egypt, the indigenous culture existed in different parts of Africa (South Africa, North Africa, etc.) in terms of visual arts, symbols and so on could be a topic to research. You can also do the research on other ancient places such as Asia, America, Australia, etc.
The effects of art on different events
You may also investigate the effects of visual arts, fine art, and generally different aspects of art on variety of events including wars, intercultural competence of people, colonization, etc. and vice versa, meaning, the effects of war, and other events on art.
Nature was an inspiring element of many artists’ works. The questions like how do you see the art of God in the nature, how can you get some ideas of nature for your art, and what was the effects of nature on ancient art could be a topic of thesis.
Note: I repeat, do not forget to limit this ideas and define your subject clearly.
Use of art in technology
How can you use art in modern technologies such as web designing, or even in military technology, medical technology, video games, etc.?
How you can make use of modern technologies for creating a piece of art?
Limit these questions and define your thesis title.
Beliefs and art
How can art have an effect on people beliefs, and vice versa?
To write your thesis title, pick a specific art and investigate its effect on a specific belief.
Using art in treatment
You can use your art for treating psychological, or even physical patients.
The evolution of art
Art has undergone a lot of changes from the era of early human until now. You can do a research on this evolution from different aspects and in terms of different art disciplines.
Skills vs. feelings
Which one is more important in creating a piece of art?
Is it possible that an untrained person creates a precious piece of art only by relying on his feeling?
Analyzing a piece of art
Everything created by people can be a piece of art; logos, paintings, even the design of furniture, equipment and so on. Pick a famous one and analyze it in detail.